White to play and capture the two black stones that cut off the two white stones.
The belly attachment does the trick.
After the continuation to , White has four liberties and Black three[1].
If Black fills outside liberties first, he loses the semeai too.
is zokusuji: a crude move which doesn't work. The best result she can get now is ko.
White protects at and loses time in the semeai. Her stones are captured.
Persevering with makes it ko. The ko is very disadvantageous for White. There is no need to make it ko if you can win unconditionally.
[1] (It is a Type 1 fight: the side with more external liberties is the favourite; the favourite kills the underdog - Richard Hunter's theory on counting liberties).
One may want to compare the problem discussed above with the following:
This problem is a different beast altogether! For the solution, see two stone corner squeeze.